The present invention relates generally to heat exchangers and more specifically to stacked fin and tube type heat exchangers.
Stacked fin and tube type heat exchangers generally are fabricated from sheet metal stock in which a plurality of protrusions are formed which are open at both ends thereof and are positioned in side by side relationship in an elongated strip of material of a width typically equal to the thickness of the desired heat exchanger. Typically, each strip will have a plurality of rows of such protrusions positioned in side-by-side spaced relationship. These strips are then cut to a desired length and stacked with the protrusions of adjacent sheets being nested together to thereby form fluid flow paths through the stacked sheets. Suitable headers are secured to opposite ends of the stacked sheets or strips and the entire assembly may then be subject to a brazing operation to thereby fixedly secure the components in fluid tight sealing relationship. Such a heat exchanger construction is shown in U.S. Pat. No. 4,509,672 issued Apr. 9, 1985 and assigned to the same assignee as the present application.
Such nested, stacked fin and tube type heat exchangers offer excellent high strength extremely durable type heat exchangers which are particularly well suited for industrial type applications such as cooling hydraulic fluids on large construction equipment. However, the volume of fluid flow through a given size heat exchanger of this type is limited because of the necessary spacing required between the respective fluid flow path defining protrusions. Further, the protrusions are formed by a relatively slow press operation which tends to be time consuming and hence relatively costly.
In another type of heat exchanger, strips of sheet stock material is folded into an accordion or corrugated pattern. The accordion strips are then stacked with the folds of each strip extending in alternating directions and flat plates being positioned therebetween. Flat bars are also placed along the sides and ends in alternating fashion for each layer to thereby define fluid flow paths. While this type of construction offers ample cross-sectional area to accommodate high volume fluid flow, the corrugated strips of one layer are only aligned with the corrugated strips of the next layer at spaced points along each fold. This arrangement thus results in an impairment of the thermal heat transfer efficiency of such heat exchangers.
The present invention, however, provides an improved heat exchanger construction in which strip type sheet stock is formed with a plurality of laterally extending troughs positioned in longitudinally spaced relationship along the length of the strip stock. In one form the bottom surface of each trough is pierced to form a plurality of louvered like openings therein. The thus formed strips maybe cut to a desired length, stacked in a nested relationship and the laterally open ends thereof closed by sealing strips. Suitable header plates may then be secured to opposite ends of the stacked strips and the entire assembly subject to a brazing operation to secure the assembly together after which header covers are secured to the header plates to complete the heat exchanger. In another embodiment a plurality of relatively large spaced openings are formed in the bottom surface of each of the troughs. The openings are positioned such that when the respective cut to length strips are stacked to form the heat exchanger core, the openings will be offset from one strip to the next to thereby impart a turbulent flow pattern to the fluid flowing therethrough. This turbulent flow pattern aids in ensuring maximum cooling of the fluid by the heat exchanger. Additionally, in some applications, the surfaces of the strips positioned between the adjacent troughs may be pierced with louver-like openings to increase heat transfer to the air flowing thereacross.
As thus formed, the troughs of the stacked strips form fluid flow paths extending across the full width of the heat exchanger thus providing a greater cross-sectional area for fluid flow for a given size heat exchanger as compared to the prior fin and tube type construction discussed above. Further, the individual strips are suited for rapid and economical fabrication by a high speed press operation or possibly at least in part by a continuous roll forming operation which minimizes the lost cycle time incurred in a reciprocating press forming operation. Additionally, the heat exchanger of the present invention is designed such that the bottom of each trough is positioned in substantially laterally aligned relationship with the intermediate fin forming portion of another strip member to thereby ensure a direct and short heat transfer path to the heat radiating fin portion. Further, the troughs are designed such that when nested, the sidewall portions thereof overlap thereby forming a double wall thickness for the fluid flow path which not only assures a high strength heat exchanger capable of handling fluids under substantial pressure but also assures a substantial surface area for creating a sealing relationship between adjacent strip members. Additionally, the double wall construction allows the use of thinner sheet stock thus facilitating the forming operation without reducing the strength of the resulting heat exchanger. The present construction is well suited for fabrication of heat exchangers from a variety of materials such as steel or aluminum and in particular for the use of materials having one or both sides coated with a cladding of a lower melting point material to facilitate brazing of the components into a fluid tight sealed relationship.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings.